1. Field of the Invention
The present invention relates to the structure of a power converter comprising a power conversion element and the structure of a semiconductor device employed for this power converter.
2. Description of the Background Art
FIG. 13 is a circuit diagram showing the structure of a conventional power converter 101. Referring to FIG. 13, the conventional power converter 101 is applied to a drive unit for an ignition coil 105. The ignition coil 105 controls an ignition plug 104 employed for the engine of an automobile. The power converter 101 individually comprises a semiconductor device 102 and another semiconductor device 103. In the semiconductor device 102, a power conversion element such as an IGBT (insulated gate bipolar transistor) 119 and Zener diodes 120 and 121 are formed on the same chip employing a silicon substrate. The IGBT 119 may be replaced with another element such as a power MOSFET or a bipolar power transistor. What kind of element is employed as the power conversion element is not important for the present invention but any one of existing elements and currently studied elements may be employed. The following description is made with reference to the IGBT employed as the power conversion element.
The Zener diodes 120 and 121 are elements specific to the drive unit for driving the ignition coil. The IGBT 119 is formed as an aggregate of small elements referred to as cells, and emitter wires for these cells are divided into two systems for intentionally causing difference between the numbers of the cells connected to the respective emitter wires. The magnitude of a current flowing in an emitter depends on the ratio of cell numbers, and hence a collector current (main current flowing in the power conversion element) of the IGBT 119 can be indirectly measured by detecting a small current having unique correlation with the current flowing in the power conversion element.
In the semiconductor 103, a difference voltage comparison circuit 109, a power supply circuit 110, a high voltage detection circuit 111, protective elements 113 and 114, a timer circuit 115, a logic gate 116, an output circuit formed by an npn transistor 117 and a negative feedback control circuit 118 are formed on the same chip employing a silicon substrate.
The difference voltage comparison circuit 109 has two input terminal, and the first input terminal is connected to a terminal 107 (control input terminal from a control unit (not shown)) of the power converter 101 through a circuit formed by a resistance and a capacitor. The second input terminal is connected to another terminal 108 (reference potential input terminal from the aforementioned control unit (not shown)) of the power converter 101 through the aforementioned circuit. The difference voltage comparison circuit 109 has a waveform shaping function exhibiting a hysteretic characteristic, in order to prevent a malfunction resulting from fluctuation of the potential of the silicon substrate employed for the semiconductor device 103. The difference voltage comparison circuit 109 is formed by a Schmidt circuit exhibiting a hysteretic characteristic and other elements.
The timer circuit 115 is provided for preventing the IGBT 119 from breakage resulting from heat generated when the IGBT 119 is continuously energized over a long period. When the IGBT 119 is continuously energized in excess of a prescribed time (several 100 ms) and the voltage of a capacitor (proportionate to the energization time for the IGBT 119) input in a positive phase input terminal of a comparator exceeds a prescribed constant voltage input in a negative phase input terminal, the timer circuit 115 regards that the quantity of heat generated from the IGBT 119 is increased and inputs a signal for stopping drive of the npn transistor 117 in the logic gate 116.
The power supply circuit 110 supplies power for driving various circuits provided in the semiconductor device 103. The battery voltage (the voltage of a battery 106) of the automobile fluctuates in a wide range (about several V to 24 V), and hence the power supply circuit 110 generating a constant power supply voltage regardless of the voltage of the battery 106 is provided in order to stably operate the timer circuit 115, a waveform shaping circuit provided in the difference voltage comparison circuit 109 and the like.
The high voltage detection circuit 111 has a function of forcibly stopping drive of the IGBT 119 when the voltage of the battery 106 is abnormally increased, in order to prevent breakage. The high voltage detection circuit 111 detects that the voltage of the battery 106 exceeds a prescribed voltage (about 30 V) and inputs a signal for stopping drive of the npn transistor 117 in the logic gate 116.
The negative feedback control circuit 118 has a function of detecting the value of the emitter current of the IGBT 119 and controlling operations of the IGBT 119 so that the main current does not flow in excess of a prescribed value. When the voltage input in the negative phase input terminal (voltage of a resistor connected to the emitter of the IGBT 119, proportionate to the emitter current) exceeds the prescribed constant voltage input in the positive phase input terminal, the negative feedback control circuit 118 inputs a signal for stopping drive of the IGBT 119 in a gate electrode of the IGBT 119.
The protective elements 113 and 114 have a function of suppressing a voltage applied to the circuit not to exceed a prescribed level, thereby protecting the circuit.
When the semiconductor device 103 drives the IGBT 119 by its control operation, a current flows toward a primary winding of the ignition coil 105 (toward the power converter 101), and a resulting primary winding voltage is multiplied by the turn ratio and transmitted toward a secondary winding of the ignition coil 105 (toward the ignition plug 104). Sparks come off between gaps of the ignition plug 104 due to this voltage to combust fuel in a cylinder (not shown) and provide motive power for the engine.
When stopping drive of the IGBT 119 and cutting off the current flowing toward the primary winding of the ignition coil 105, energy stored in the ignition coil 105 generates force (counter electromotive force) stepping up a collector voltage of the IGBT 119 to the positive direction. When a voltage exceeding a reverse withstand voltage of the Zener diode 120 is caused, the Zener diode 120 operates to increase a gate voltage of the IGBT 119 and drive the OFF-state IGBT 119 as a result. Thus, the collector voltage is kept in a constant state.
In the conventional power converter 101 shown in FIG. 13, however, a number of circuits such as the difference voltage comparison circuit 109, the timer circuit 115, the negative feedback control circuit 118 and the like are formed in the semiconductor device 103 to disadvantageously increase the circuit scale of the semiconductor device 103 in particular.
According to a first aspect of the present invention, a power converter comprises: a first semiconductor device including a first semiconductor substrate and a power conversion element formed on the first semiconductor substrate; and a second semiconductor device formed on a second semiconductor substrate different from the first semiconductor substrate for generating a control signal for controlling drive of the power conversion element and inputting the control signal in the first semiconductor device on the basis of a signal input from an external control unit.
According to a second aspect of the present invention, in the first aspect, the first semiconductor device further includes a cutoff circuit formed on the first semiconductor substrate for detecting the temperature of the first semiconductor substrate on a portion formed with the power conversion element and stopping drive of the power conversion element when the temperature exceeds a prescribed level.
According to the second aspect, the cutoff circuit directly detects heat generated from the power conversion element and stops drive of the power conversion element on the basis of the result of detection. As compared with a power converter employing a timer circuit stopping drive of a power conversion element in response to a continuous energization time for the power conversion element, therefore, the power conversion element can be more effectively prevented from a failure resulting from heat generation.
Further, the cutoff circuit can be formed more simply than the timer circuit, whereby the structure of the overall power converter can also be simplified.
According to a third aspect of the present invention, in the first aspect, the first semiconductor device further includes a waveform shaping circuit exhibiting a hysteretic characteristic, formed on the first semiconductor substrate, and the waveform shaping circuit operates with drive power of a potential input in its own input terminal.
According to the third aspect, the waveform shaping circuit may be provided with no power supply terminal for externally supplying drive power, whereby the circuit structure can be simplified as compared with a waveform shaping circuit driven by externally supplied power.
According to a fourth aspect of the present invention, in the first to third aspects, the second semiconductor device has an output circuit for outputting the control signal, formed on the second semiconductor substrate, and the output circuit is formed by a pnp transistor or a p-channel MOSFET formed in an n-type semiconductor layer.
According to the fourth aspect, the pnp transistor or the p-channel MOSFET can be inhibited from an erroneous operation also when the potential of the second semiconductor substrate is transitionally increased while the pnp transistor or the p-channel MOSFET is in an OFF state.
According to a fifth aspect of the present invention, in the first to fourth aspects, the first semiconductor device and the second semiconductor device individually include GND terminals supplied with GND levels.
According to the fifth aspect, a malfunction following fluctuation of the potential of the second semiconductor substrate resulting from a main current of the power conversion element can be suppressed by forming a Schmidt circuit simply comparing a voltage input in a positive phase input terminal and a constant voltage input in a negative phase input terminal with each other on the second semiconductor substrate.
According to a sixth aspect of the present invention, in the fifth aspect, the power converter further comprises a voltage limiting circuit limiting a potential difference between the GND level of the first semiconductor device and the GND level of the second semiconductor device within a prescribed value.
According to the sixth aspect, a malfunction resulting from abnormally large potential difference between the GND level of the first semiconductor device and the GND level of the second semiconductor device can be suppressed so that the power converter causes a smaller number of malfunctions.
According to a seventh aspect of the present invention, in the sixth aspect, the voltage limiting circuit is formed on the second semiconductor substrate.
According to the seventh aspect, the number of components can be reduced as compared with the case of forming the voltage limiting circuit as a component independent of the second semiconductor device.
According to an eighth aspect of the present invention, a power converter comprises a first semiconductor device having a power conversion element formed on a first semiconductor substrate and a second semiconductor device formed on a second semiconductor substrate different from the first semiconductor substrate for generating a control signal for controlling drive of the power conversion element and inputting the control signal in the first semiconductor device on the basis of a signal input from an external control unit, while the first semiconductor device and the second semiconductor device individually include GND terminals supplied with GND levels.
According to the eighth aspect, a malfunction following fluctuation of the potential of the second semiconductor substrate resulting from a main current of the power conversion element can be suppressed by forming a Schmidt circuit simply comparing a voltage input in a positive phase input terminal and a constant voltage input in a negative phase input terminal with each other on the second semiconductor substrate.
According to a ninth aspect of the present invention, in the eighth aspect, the power converter further comprises a voltage limiting circuit limiting a potential difference between the GND level of the first semiconductor device and the GND level of the second semiconductor device within a prescribed value.
According to the ninth aspect, a malfunction resulting from abnormally large potential difference between the GND level of the first semiconductor device and the GND level of the second semiconductor device can be suppressed so that the power converter causes a smaller number of malfunctions.
According to a tenth aspect of the present invention, in the ninth aspect, the voltage limiting circuit is formed on the second semiconductor substrate.
According to the tenth aspect, the number of components can be reduced as compared with the case of forming the voltage limiting circuit as a component independent of the second semiconductor device.
According to an eleventh aspect of the present invention, a semiconductor device comprises a semiconductor substrate, a power conversion element formed on the semiconductor substrate and a cutoff circuit formed on the semiconductor substrate for detecting the temperature of the semiconductor substrate on a portion formed with the power conversion element and stopping drive of the power conversion element when the temperature exceeds a prescribed level.
According to the eleventh aspect, the cutoff circuit directly detects heat generated from the power conversion element and stops drive of the power conversion element on the basis of the result of detection. Therefore, the power conversion element can be more effectively prevented from a failure resulting from heat generation.
According to a twelfth aspect of the present invention, in the eleventh aspect, the semiconductor device further comprises a waveform shaping circuit exhibiting a hysteretic characteristic, formed on the semiconductor substrate, while the waveform shaping circuit operates with drive power of a potential input in its own input terminal.
According to the twelfth aspect, the waveform shaping circuit may be provided with no power supply terminal for externally supplying drive power, whereby the circuit structure can be simplified as compared with a waveform shaping circuit driven by externally supplied power.
According to a thirteenth aspect of the present invention, a semiconductor device comprises a semiconductor substrate of a first conductivity type, a semiconductor layer of a second conductivity type, different from the first conductivity type, formed on the semiconductor substrate, a first Zener diode having a first electrode defined by a first impurity-introduced region of the first conductivity type formed in the semiconductor layer and a second electrode defined by a second impurity-introduced region of the second conductivity type formed in the semiconductor layer, a second Zener diode having a first electrode defined by a third impurity-introduced region of the first conductivity type formed in the semiconductor layer and a second electrode defined by a fourth impurity-introduced region of the second conductivity type formed in the semiconductor layer and connected to the second electrode of the first Zener diode, and a wire formed on a main surface of the semiconductor layer for fixing the potential of the semiconductor layer.
According to the thirteenth aspect, it is possible to avoid drive of a parasitic transistor having an emitter defined by the semiconductor substrate, a base defined by the semiconductor layer and a collector defined by the third impurity-introduced region by fixing the potential of the semiconductor layer to a level exceeding the reverse voltage of the first Zener diode by the wire.
An object of the present invention is to obtain a power converter capable of reducing the circuit scale as a whole and a semiconductor device employed for this power converter.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.